Non-Invasive Battery Recharger for Electronic Cardiac Implants

ABSTRACT

The present invention refers to a device used to recharge the battery of electronic cardiac implants, like implanted pacemakers and defibrillators. It can be used to recharge the battery after an emergency requirement, such as: defibrillation or in diagnosis and or reprogramming of implants, during which no energy is demanded from the internal battery, seeing that the energy feed becomes guaranteed (accepted) by the proposed device. The invention is composed by three essential components: a generator (A), a transmitter unit (B) and a receptor coil (C). The generator is destined to produce an energy signal with determined amplitude and frequency and that is carried across through a coaxial cable to the transmitter unit (B). The emitted magnetic field is captured by the receptor coil (C) that is implanted inside the human body, generating a voltage with the absence of the Gibbs phenomenon. Furthermore, the battery recharging device guarantees the energetic supply of a communication channel between the exterior for diagnosis and/or implant reprogramming. In this case, there will be no demand of energy from the internal battery.

The present invention turns possible the battery recharging of cardiacimplants, like implanted pacemakers and defibrillators, allowing alonger life for the internal battery in the human body, and postponingthe customary chirurgic intervention for replacement.

The energy consumption of the cardiac implants varies according to itsfunction, this being determined by the pathology and activity of thepatient.

The duration of the cardiac implant battery varies from 3 to 9 years,being essentially determined by the electrical energy consumption.

The electrical energy consumption, not considering the scale factorreferring to the voltage amplitude, is proportional to the productbetween the medium electrical current value and the interval of timeduring which the same persists. This product characterises theelectrical charge that moves from the battery to the implant'selectronic circuit.

During the progress that accompanies the scientific investigation in themedical and in the electronic fields more and more sophisticatedimplants are emerging, in terms of functionality and in signalprocessing speed.

The assisted reprogramming, the defibrillation and periodic monitoringof the implant activity are some of those potentials.

The proposed configuration offers the possibility to access and changethe implant's functionality algorithmic structure, without energyconsumption of the internal battery, since the energetic supply is nowguaranteed by the proposed device.

Actually there is no known process that permits the recharge of thebattery. One of the prevention factors to achieve the energetic transferto the implant's interior through a non-invasive process is the greatdistance that separates the implant from the exterior transmitter.

To overcome this obstacle in nowadays technology there are solutionsbased on switched power supplies which basic functionality principle isset on the impulse modulation technique (PWM—pulse width modulation). Inthese types of sources the form of voltage outgoing wave is affected bythe variation of the width of the impulse.

However, this technique is associated to an effect known as the Gibbsphenomenon: it consists in an increased importance of the high-frequencyelectromagnetic noise in the, which can be quantified by Fourieranalysis.

This high-frequency electromagnetic noise is detected by the implantselectronic circuits, resulting in data/signal misinterpretation and/orerroneous decisions resulting from the algorithmic implants processing,with the obvious consequences for the patient.

It is precisely these inconveniences that characterise the actual stateof the technique. Or else let us observe:

Reference US2005075696 refers to the use of an oscillatory current whichwill induce a voltage to the terminals of a secondary coil, notspecifying which and not considering the electromagnetic interferenceseffect.

References US2005037256 and FR2420832 does not comment about the primarycurrent, referring only to the use of a diode in the net (169) and (6),respectively, which represents poor energy efficiency for each cycle ofthe secondary voltage. In this case, a full wave rectification could beused, instead of the half-wave rectification.

Proposal DE2720331 is similar to the ones described in the aboveparagraph. However, it shows an inaccuracy in the schematic in the diode(6) and/or battery (2) polarity.

Reference JP2002315209 does not specify the waveform of the primaryvoltage and, from the presented schematic, the production of EMI noiseis not excluded.

The same applies to reference U.S. Pat. No. 5,411,537, which also doesnot predict the primary voltage wave form.

On the other hand, the proposal EP0473957 presents a solution that doesnot consider the Gibbs phenomenon, besides the evidence of the necessityto use the detector (84), to measure phase difference or frequencydifference. In this way, this proposal admits the existence of frequencycomponents distinct form the fundamental.

The Prototype described in FIG. 1a of in Reference GB1419531 presents anefficient solution to process the full period of the secondary voltage,using the rectifier bridge (30), the sensing resistor (32) and the FET(31). However, from the auxiliary coil we verify that the frequencycontrol of the energy carrier signal (which is also not specified, as inthe above examples) is determined by the pacemaker with a tuned receptorexcited by the coil (20 b).

Summarising, the conceptions which characterise the state of the artdoes not attend to the Gibbs phenomenon. Consequently, the electronicunit of the implant is exposed to unacceptable EMI levels.

The present invention is composed by three essential components: agenerator, a transmitter unit and a coil receptor.

Besides that, it does not need any feedback network for the processcontrol, simplifying its use.

This invent does not permit the appearance of the Gibbs phenomenon,since the energy signal carrier wave is (co)sinusoidal and the suppliedresonant network is linear. Thus, the effect of eventual electromagneticinterferences does not apply since the energy carrier signal as a knownand allowed frequency in the communication channel.

Nevertheless, the utilisation of the sinusoidal signals contributes tothe appearance of the reactive components of the electrical currentscoming from the resonance network. Consequently, a supplementaldissipative effect occurs at the output power circuit of the generatorand an increase of the energy consumption, representing less efficiencyof energy transfer.

The form found and explored to overcome this problem consists inminimising the flow of reactive energy circulating in the resonantnetwork.

By minimizing the reactive energy transit, a reduction/exclusion of theoutput current reactive component is achieved, resulting in less powerdissipation—Joule effect—in the generator stage. In these conditions theresonant network is purely resistive.

The invention optimises the reactive energy flow determined by theregime of exploration previewed at the Predictor—Corrector Abacusillustrated in FIG. 1.

The Predictor—Corrector Abacus is a representation in the complex planof a situation where a specific load is supplied by an electrical energyto the Active Power P, and Reactive Power Q. The energy is submittedunder a nominal voltage U in forced alternated sinusoidal condition at afrequency f.

What characterises this Abacus is the circumstance of considering theeffect of the reactance and the resistance of longitudinal transmissionlines, that is evident at the figure by the position of the angles ofsegment line that proliferate in the I and II quadrants of the Argand'scomplex plan, of the complex plan relative from the axis of the base.The effect of these parameters is presented in the synchronised rotationof segment line around the affix z₁=1+j0.

The affix z₂, represents the relations between the input and the outputvoltages. The unit radius of the circle corresponds to the points of thecomplex plan where |z₂|=1. The family of lines p, represents thegeometric place of situations that correspond to the value of the activepower P. However the lines q, characterise the situations thatcorrespond to the Reactive Power Q.

The general equation for line p is

$y = {{{- \frac{R_{l}}{X_{l}}}x} + \frac{R_{l}}{X_{l}} + {( \frac{P}{U^{2}} )( \frac{Z_{l}^{2}}{X_{l}} )}}$

On the other hand, lines q represents the situations corresponding tothe reactive power Q.

The general equation of line q is

$y = {{\frac{X_{l} - {R_{l}{tg}\; \phi}}{R_{l} + {X_{l}{tg}\; \phi}}( {x - 1} )} + {( \frac{Z_{l}^{2}}{R_{l} + {X_{l}{tg}\; \phi}} )\omega \; C}}$

Lines q turn by an angle φ, corresponding to a phase difference betweenload voltage and current, starting from a point in the p line, with P=0.

The intersection of two lines p and q define the operating point and thevoltage relation.

The mathematics model that presents the Abacus is defined by thefollowing equation:

${1 + \overset{\_}{p}} = {\overset{\_}{m} = {\sqrt{\begin{matrix}{\lbrack {1 + ( \frac{{PR}_{l} + {QX}_{l}}{U^{2}} ) - {\omega \; X_{l}C}} \rbrack^{2} +} \\\lbrack {1 + ( \frac{{PR}_{l} - {QX}_{l}}{U^{2}} ) - {\omega \; R_{l}C}} \rbrack^{2}\end{matrix}}\mspace{11mu} ^{j{\{{{arctg}{\lbrack\frac{{(\frac{{PR}_{l} - {QX}_{l}}{U^{2}})} - {\omega \; R_{l}C}}{1 + {(\frac{{PR}_{l} + {QX}_{l}}{U^{2}})} - {\omega \; X_{l}C}}\rbrack}}\}}}}}$

Where m the voltage ratio and p represents the losses factor.

The parameters that characterise the line are parameters distributedthroughout their whole extension.

Centralizing the parameters of the distributed model in a compact coil,we obtain the representation of the reactance X_(l) by concentratedparameters that consists the present transmission unit of thisinvention.

Thus, the transmitter unit resembles to a compact transmission line.

An additional advantage also becomes important, reported by theutilisation of the (co) sinusoidal signal. It consists on the focuseffect which is obtained by the electromagnetic resonance phenomenon andthat overcomes the high magnetic reluctance characterised by the longdistance between the coil receptor and the transmitter unit.

FIG. 2 represents the block diagram of the device. The energy supply isprovided by the energy supply cable (1), by the alternating voltage fromthe energy public network, or by a direct current supply, the cigarettelighter plug of an automobile.

The converter (2) is used to supply the symmetrical voltages to theoscillator (3) and to the amplifier (6). Additionally, it supplies theinductor (8) of the transmitter unit (B), by the manual switch (14), inorder to achieve a stationary magnetic field to instantly inhibit thepacemaker.

Potentiometer (4) adjust the frequency of the voltage controlledoscillator (VCO) (3), in order to minimize the reactive energy transfer,which can be visualized by the light sign (13).

The magnetic field intensity is adjusted through the potentiometer (5).Block (6) is the integrated hybrid amplifier that supplies the resonantnetwork composed by the capacitor (7) and the primary coil (8), whichconstitutes the transmitter unit.

The magnetic field produced by this unit induces an alternating voltagein the coil terminals (9), which after rectification in the rectifierbridge (10), supplies the implant electronic circuit through the diode(11). This diode circumvents the implant battery from discharging in theequivalent leakage resistance.

The longitudinal resistance is majored by a value related to the skineffect, R(ω), determined by the depth of penetration

$\delta = \sqrt{\frac{2}{\omega\mu\sigma}}$

and that characterises the dependence of the resistance behaviour on thefrequency. The resistance varies from a value measured at direct currentR₀, until R(ω).

On the same way the coil reactance depends on the frequency and alsovaries with magnetic reluctance, which is affected by the distancebetween coils. However, dispersion characterises a situation of maximumreluctance, which limits the circulating current in the compensationnetwork.

Maxwell equation div {right arrow over (B)}=0 characterises thedispersion of the field lines which close in the shortest path of thecoil magnetic circuit. In this way, we identify a non-evasive behaviour(without leakage, control losses or limitation).

The control is efficient when m varies 75°<θ<90°, which andgeometrically φ+θ=90°, corresponds to 0<φ<15°. The correspondent powerfactor, cos φ, varies between 0.96 e 1.

The situation correspondent to θ=90°, occurs at x=0. In this case, theideal situation φ=0° e P=0, results from the equality between equationsp e q the following:

$y_{P} = {{{{- \frac{R_{l}}{X_{l}}}x} + \frac{R_{l}}{X_{l}} + {( \frac{P}{U^{2}} )( \frac{Z_{l}^{2}}{X_{l}} )}} = {{{- \frac{R_{l}}{X_{l}}}x} + \frac{R_{l}}{X_{l}}}}$$\begin{matrix}{y_{Q} = {{\frac{X_{l} - {R_{l}{tg}\; \phi}}{R_{l} + {X_{l}{tg}\; \phi}}( {x - 1} )} + {( \frac{Z_{l}^{2}}{R_{l} + {X_{l}{tg}\; \phi}} )\omega \; C}}} \\{= {{\frac{X_{l}}{R_{l}}( {0 - 1} )} + {( \frac{Z_{l}^{2}}{R_{l}} )\omega \; C}}} \\{= {{- \frac{X_{l}}{R_{l}}} + {( \frac{Z_{l}^{2}}{R_{l}} )\omega \; C}}}\end{matrix}$$y_{P} = { y_{Q}\Leftrightarrow{{{- \frac{R_{l}}{X_{l}}}x} + \frac{R_{l}}{X_{l}}}  = { {{- \frac{X_{l}}{R_{l}}} + {( \frac{Z_{l}^{2}}{R_{l}} )\omega \; C}}\Leftrightarrow X_{l}  = { \frac{1}{\omega \; C}\Leftrightarrow L_{l}  = \frac{1}{\omega^{2}C}}}}$

The tuning frequency is obtained from

$\omega^{2} = { \frac{1}{L_{l}C}\Leftrightarrow f_{0}  = \frac{1}{2\pi \sqrt{L_{l}C}}}$

The situation when θ=75°, occurs when lines p e q are perpendicular andline q crosses origin, which means

${{- \frac{R_{l}}{X_{l}}}x} = { {- \frac{R_{l} + {X_{l}{tg}\; \phi}}{X_{l} - {R_{l}{tg}\; \phi}}}\Leftrightarrow\phi  = { 0\Rightarrow y_{Q}  = {{{\frac{X_{l}}{R_{l}}( {x - 1} )} + \ldots} = {{{\frac{X_{l}}{R_{l}}x}\therefore{\arg \{ \overset{\_}{m} \}}} = {{{arctg}( \frac{X_{l}}{R_{l}} )} = {{\arg \; {{tg}( \frac{\omega \; L_{l\;}}{r_{0} + {l\; {\pi\Phi}\; \delta}} )}} = {{{arctg}( \frac{\omega \; L_{l}}{r_{0} + {l\; \pi \; {\Phi ( \frac{2}{\omega \; {\mu\sigma}} )}}} )} \approx {75{^\circ}}}}}}}}}$

The induced voltage in the implanted coil is high when φ=0 and its valueis given by

${{U_{1}( \frac{n_{2}}{n_{1}} )}( \frac{\omega \; L_{l}}{r_{0} + {l\; \pi \; {\Phi ( \frac{2}{\omega \; {\mu\sigma}} )}}} )} = {{{U_{1}( \frac{n_{2}}{n_{1}} )}( \frac{X_{l}}{R_{l}} )} = {{U_{1}( \frac{n_{2}}{n_{1}} )}Q}}$

where:

U₁, (n₁/n₂) and Q, represents the RMS generator's voltage, the ratio ofturns of the implanted/transmitter coils and the quality factor of thecoil, respectively.

The implanted coil is located around the leakage line of the implant orin its interior, as depicted in FIGS. 9 and 10 respectively.

FIG. 3 indicates one of the possible applications of this invention. Thegenerator unit is located in a fixed structure, like a table, shelf,etc. The transmitter unit should be located through an articulated armwith a support for example in a chair or even a bed. A flexible coaxialcable allows the connection between the generator and the transmitterunit, which by a simple but efficient location over the patient thorax,allows the energy transfer to the human body.

The position of switch (14) indicated in FIG. 2 determines if themagnetic field created by the transmitter coil is (co) sinusoidal,B=B_(máx)×sen(ωt) or stationary, B=B_(DC), respectively, if the coilcurrent is supplied by the amplifier (6) or by the direct current supply(2). If the field is stationary, the transmitter unit works like amagnet, allowing the implant command in a way that it can suspendactivity (magnetic mode); if the alternating field is selected, theimplant is recharged.

FIG. 4 represents the power supply scheme (2) indicated in FIG. 2, withthe input and rectification blocks (a) e (b), the blocks (d), (e) e (f)that constitutes the flyback converter the rectifying block (h), thefiltering block (g) and the regulating block e current limiter (q) usedto excite the transmitter coil through a direct current, which willcreate a stationary induced field B=B_(DC), similar to the one producedby a permanent magnet.

FIG. 5 represents the voltage controlled oscillator (3), identified inFIG. 2, and used to produce a (co) sinusoidal signal with frequencyproportional to the control voltage, manually adjusted by thepotentiometer (4). The mean value corresponds to the resonant frequencyof the transmitter unit resonant network.

FIG. 6 represents the power amplifier with symmetric supply (6), whichamplifies the signal generated at the voltage controlled oscillator (3)from FIG. 5, and let it available at the output plug (p).

The scheme in FIG. 7 corresponds to the transmitter unit with a resonantcapacitor (7), the coil (8), responsible for the magnetic fieldgeneration, a neon sign (13) and a plug (q) to connect to the generatorunit (A) through plug (p), shown in FIG. 2.

The implanted unit represented in FIG. 8 is constituted by the implantedcoil (9) located in the periphery of the implant or in its interior andwith the terminals connected to the rectifier bridge (10), which in turnare connected to the filter capacitor (11) e to the protection diode(12), which prevents the battery from discharging in the equivalentleakage resistance.

The assembly of the sensor coil (9) is suggested in FIGS. 9 and 10,respectively, by its location in the periphery or in the interior of theimplant.

1. Device used to recharge the battery of cardiac implants,characterized by a generator (A) destined to produce a (co)sinusoidalsignal with frequency adjusted by a potentiometer (5), in turn of a meanvalue designated by resonant frequency, which envisage the minimizationof the reactive energy transit in the resonant network (B), composed bya capacitor (7) and by a coil with air nucleus (8), which characteristicvalues determine the resonant frequency and constitutes the transmitterunit, destined to produce a stationary magnetic field or alternatedsinusoidal, for the magnetic mode, or for the battery recharging,respectively, which will induce a voltage at the terminal of theimplanted coil, established at the implant periphery, in which lays therectifier block (10), the filter capacitor (11), and the diode toprotect against the inverse leakage current (12).
 2. Device according toclaim 1, characterised by converting the input electrical voltage, bythe public electric network or by a voltage available at the automobilebattery, by mean of a rectifier bridge (a), resistance (b), andcapacitor (c), applied to the transformer (d), excited by the transistor(e), controlled by the integrated circuit (f), which samples thecontinuous voltage delivered by the symmetric voltage at the rectifierbridge (h), through the secondary of (d) and filtered by the capacitorpair (g), destined to the supply of the circuits and produce a directcurrent in order to create a stationary magnetic field, destined to thefunctionality of the implant in the magnetic mode.
 3. Device accordingto claims 1 and 2, characterised by an input plug destined to supply bythe cigarette lighter of an automobile, selectable by the switch (15).4. Device according to claims 1 and 2, characterised by the oscillator,constituted by the integrated circuit (3), supplied symmetrically, whichproduces a sinusoidal signal with central oscillating frequency,characterized by the resonant coil value (8) and capacitor (7), whichdetermines the maximum energy flux generated by the amplifier (6). 5.Device according to claims 1 to 3, characterised by a button thatcommands the potentiometer to adjust the oscillator frequency (3),destined to achieve the resonant and maximum transfer condition,corresponding to φ=0°.
 6. Device according to claim 1 to 3,characterised by an amplifier block constituted by a hybrid integratedcircuit (6), with symmetric feed, excited by the oscillator signal (3)through the potentiometer (5) and accessible at the secure shieldedoutput.
 7. Device according to claim 1 to 5, characterised by a buttonthat commands the potentiometer (5), destined to adjust the magneticfield amplitude, created according to the implant depth.
 8. Deviceaccording to claim 1 to 6, characterised by producing a magnetic fieldthrough the transmitter unit (B), which includes a coil with air nucleus(8) and the resonant capacitor (7), fed by the connector (q), providedwith a neon indicator lamp (13) signalising optimal condition.
 9. Deviceaccording to claim 1, characterised by a switch (14) destined to selectthe operating mode, to works in the magnetic mode, destined to suspendthe implant activity, or to works in the battery recharging mode. 10.Device according to claim 1, characterised by receiving the magneticenergy emitted by the transmitter unit through the planar receptor coil,which supplies the rectifier bridge, constituted by four fast-recoverydiodes (10), destined to produce a continuous voltage by full waverectification, filtered by the capacitor (11), and applied to theimplant supply circuit through the diode (12), which avoids the eventualbattery discharging to the equivalent leakage resistance.